This invention relates in general to method and apparatus for preventing the overflow of liquid from between flexible layers on a solid surface and, more particulary, their use in an improved photoelectrophoretic web imaging device.
In the photoelectrophoretic imaging process, monochromatic including black and white or full color images are formed through the use of photoelectrophoresis. An extensive and detailed description of the photoelectrophoretic process is found in U.S. Pat. Nos. 3,384,488 and 3,384,565 to Tulagin and Carreira; 3,383,993 to Yeh and 3,384,566 to Clark, which disclose a system where photoelectrophoretic particles migrate in image configuration providing a visual image at one or both of two electrodes between which the particles suspended within an insulating carrier is placed. The particles are electrically photosensitive and are believed to bear a net electrical charge while suspended which causes them to be attracted to one electrode and apparently undergo a net change in polarity upon exposure to activating electromagnetic radiation. The particles will migrate from one of the electrodes under the influence of an electric field through the liquid carrier to the other electrode.
The photoelectrophoretic imaging process is either monochromatic or polychromatic depending upon whether the photosensitive particles within the liquid carrier are responsive to the same or different portions of the light spectrum. A full-color polychromatic system is obtained, for example, by using cyan, magenta and yellow colored particles which are responsive to red, green and blue light respectively.
In photoelectrophoretic imaging generally, and as employed in the instant invention, the important broad teachings in the following four paragraphs should be noted.
Preferably, as taught in the four patents referred to above, the electric field across the imaging suspension is applied between electrodes having certain preferred properties, i.e., an injecting electrode and a blocking electrode, and the exposure to activating radiation occurs simultaneously with field application. However, as taught in various of the four patents referred to above and Luebbe et al., U.S. Pat. No. 3,595,770; Keller et al., U.S. Pat. No. 3,647,659 and Carreira et al., U.S. Pat. No. 3,477,934; such a wide variety of materials and modes for associating an electrical bias therewith, e.g., charged insulating webs, may serve as the electrodes, i.e., the means for applying the electric field across the imaging suspension, that opposed electrodes generally can be used; and that exposure and electric field applying steps may be sequential. In preferred embodiments herein, one electrode may be referred to as the injecting electrode and the opposite electrode as the blocking electrode. This is a preferred embodiment description. The terms blocking electrode and injecting electrode should be understood and interpreted in the context of the above comments throughout the specification and claims hereof.
It should also be noted that any suitable electrically photosensitive particle may be used. Kaprelian, U.S. Pat. No. 2,940,847 and Yeh, U.S. Pat. No. 3,681,064 disclose various electrically photosensitive particles, as do the four patents referred to above.
In a preferred mode, at least one of the electrodes is transparent, which also encompasses partial transparency that is sufficient to pass enough electromagnetic radiation to cause photoelectrophoretic imaging. However, as described in Weigh, U.S. Pat. No. 3,616,390 both electrodes may be opaque.
Preferably, the injecting electrode is grounded and the blocking electrode is biased to provide the field for imaging. However, such a wide variety of variations in how the field may be applied can be used, including grounding the blocking electrode and biasing the injecting electrode, biasing both electrodes with different bias values of the same polarity, biasing one electrode at one polarity and biasing the other at an opposite polarity of the same or different value, that just applying sufficient field for imaging can be used.
The photoelectrophoretic imaging system disclosed in the above-identified patents may utilize a wide variety of electrode configurations including a transparent flat electrode configuration for one of the electrodes, a flat plate or roller for the other electrode used in establishing the electric field across the imaging suspension.
There has been recently developed a photoelectrophoretic imaging system which utilizes web materials, which optimally may be disposable. In this process, the desired, e.g., positive image, is formed on one of the webs and another web will carry away the negative or unwanted image. The positive image can be fixed to the web upon which it is formed, or the image transferred to a suitable backing such as paper. The web which carries the negative image can be rewound and later disposed of. In such photoelectrophoretic imaging systems employing disposable webs, cleaning systems are not required.
In a photoelectrophoretic web imaging device, an about 1 mil coating of imaging suspension may be coated on the conductive or injecting web and brought into contact with a second web, referred to as a blocking web, to form an ink-web sandwich at the imaging zone whereat, the ink is subjected to an electrical field and image exposure. When the electrical field is applied across the ink-web sandwich, there is a tendency for suspension to be uniformly squeezed out from between the webs to the side edges of the webs. If this overflow is not curtailed or prevented, this overflow liquid transfers to the imaging roller and in turn starts to work its way back between the roller and web and may thereby degrade the quality of images produced.
Apparatus in which liquid trapping systems are generally disclosed, British Patent Publication 1,326,786, published Aug. 15, 1973, discloses electrophoretic apparatus for preventing liquid overflow. In the British device, a drum which supports a photosensitive member is provided with annular grooves along the outside edges of the drum and outside the edges of the photosensitive member. In applicant's device, annular grooves are provided on the roller inside the edges of the two support members.
Overflow prevention devices are also found in the camera art. For example, E. H. Land, U.S. Pat. No. 2,627,460, issued Feb. 3, 1953, shows a trap for the reception and holding of excess liquid composition used for development of the film in the Land camera; Land, U.S. Pat. No. 2,686,716, issued Aug. 17, 1954, discloses a liquid trapping device in a camera film unit which collects excess liquid after the main portion of the liquid is spread between two liquid containing layers by rupturing a container between pressure rollers. A collar having a height on the order of the thickness desired for the layer of liquid to cover the image area is provided on each end of the rollers to prevent the spreading of liquid into other parts of the camera. Other techniques to prevent the overflow of liquid in the photographic art are found in U.S. Pat. Nos. 2,627,470; 2,868,717; 2,689,243 and 3,320,065. The device of applicant's invention is a simple and improved system to prevent the overflow of liquid from between flexible layers on a solid surface and for application in photoelectrophoretic web devices.